Method and apparatus for transmitting data in wireless lan system

ABSTRACT

Disclosed are a method and an apparatus for transmitting data in a wireless LAN system. The method for transmitting data comprises the steps of: generating a discontinuation request frame for requesting discontinuation of transmitting a data frame from a master-access point to a relay device; and transmitting the discontinuation request frame to the master-access point. As a result, the occurrence of a buffer overflow in the relay device can be prevented.

TECHNICAL FIELD

The present invention generally relates to data transmission technologyin a wireless local area network (WLAN) system and, more particularly,to a method and apparatus for transmitting data to an end terminal in aWLAN system including a relay device.

BACKGROUND ART

With the development of information and communication technology,various wireless communication technologies have been developed. Amongthese technologies, a wireless local area network (WLAN) denotestechnology for allowing wireless access to the Internet in homes,businesses or specific service areas using a mobile terminal such as apersonal digital assistant (PDA), a laptop computer, a portablemultimedia player (PMP), a smart phone, or a tablet PC, based on radiofrequency (RF) technology.

Standards for WLAN technology have been developed as Institute ofElectrical and Electronics Engineers (IEEE) 802.11 standards. WLANtechnology conforming to the IEEE 802.11a standard is operated based onan orthogonal frequency division multiplexing (OFDM) scheme, and iscapable of providing a maximum data rate of 54 Mbps in a 5 GHz band.WLAN technology conforming to the IEEE 802.11b standard is operatedbased on a direct sequence spread spectrum (DSSS) scheme, and is capableof providing a maximum data rate of 11 Mbps in a 2.4 GHz band. WLANtechnology conforming to the IEEE 802.11g standard is operated based onthe OFDM or DSSS scheme, and is capable of providing a maximum data rateof 54 Mbps in a 2.4 GHz band.

WLAN technology conforming to the IEEE 802.11n standard is operatedbased on the OFDM scheme in a 2.4 GHz band and a 5 GHz band, and iscapable of providing a maximum data rate of 300 Mbps for four spatialstreams when a Multiple-Input Multiple-Output OFDM (MIMO-OFDM) scheme isused. WLAN technology conforming to the IEEE 802.11n standard maysupport a channel bandwidth of up to 40 MHz and is capable of providinga maximum data rate of 600 Mbps in that case.

As the popularization of such WLAN technology has been activated andapplications using WLANs have been diversified, the requirement for newWLAN technology that supports throughput higher than that of existingWLAN technology is increasing. Very high throughput (VHT) WLANtechnology is proposed technology that supports a data rate of 1 Gbps ormore. Meanwhile, in a system based on such WLAN technology, a problemarises in that, as the distance between WLAN devices increases,communication efficiency is deteriorated.

DISCLOSURE Technical Problem

An object of the present invention to solve the above problems is toprovide a data transmission method for improving the efficiency of aWLAN system.

Another object of the present invention to solve the above problems isto provide a data transmission apparatus for improving the efficiency ofa WLAN system.

Technical Solution

In accordance with an embodiment of the present invention to accomplishthe above objects, a communication system based on WLAN technologyincludes a certain terminal acting as a relay device for relaying datatransmitted between a master access point and an end terminal.

Here, a data transmission method performed by the relay device accordingto an embodiment of the present invention includes generating a suspendrequest frame that requests suspension of transmission of a data framefrom the master access point to the relay device, and transmitting thesuspend request frame to the master access point.

Here, the suspend request frame may be an acknowledge (ACK) frame thatis a response to a data frame received from the master access point, andthe ACK frame may include information indicating that the relay deviceis operated in a doze mode.

Here, the suspend request frame may be a null data frame that includesinformation indicating that the relay device is operated in a doze mode.

Here, the suspend request frame may include information about a suspendduration during which transmission of a data frame is suspended.

A data transmission method performed by a relay device according toanother embodiment of the present invention to accomplish the aboveobjects includes generating a resume request frame that requestsresumption of transmission of a data frame from a master access point tothe relay device, and transmitting the resume request frame to themaster access point.

Here, the data transmission method may further include receiving a dataframe, as a response to the resume-request frame, from the master accesspoint, and transmitting an acknowledge (ACK) frame, as a response to thedata frame, to the master access point.

Here, the resume request frame may be a power save (PS)-Poll frame or atrigger frame indicating that the relay device is operated in an awakemode.

Here, the resume request frame may be a null data frame that includesinformation indicating that the relay device is operated in an awakemode.

Here, transmitting the resume request frame to the master access pointmay be configured to transmit the resume request frame to the masteraccess point when it is determined that data to be transmitted to therelay device is buffered in the master access point, based on a beaconframe received from the master access point.

Advantageous Effects

In accordance with the present invention, the wireless transmissionefficiency of a WLAN system can be improved.

DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing an embodiment of a station forperforming methods according to the present invention;

FIG. 2 is a conceptual diagram showing an embodiment of theconfiguration of a WLAN system conforming to IEEE 802.11;

FIG. 3 is a flowchart showing a terminal association procedure in aninfrastructure BSS;

FIG. 4 is a conceptual diagram showing the infrastructure BSS of a WLANsystem;

FIG. 5 is a block diagram showing an embodiment of a hierarchical AIDstructure;

FIG. 6 is a block diagram showing an embodiment of the structure of aTIM information element (IE);

FIG. 7 is a block diagram showing an embodiment of the structure of aTIM encoded on a block basis;

FIG. 8 is a flow diagram showing an embodiment of a datatransmission/reception procedure;

FIG. 9 is a conceptual diagram showing a WLAN system including relaydevices;

FIG. 10 is a block diagram showing the logical configuration of a relaydevice;

FIG. 11 is a conceptual diagram showing a data transmission method in aWLAN system including a relay device;

FIG. 12 is a flowchart showing a data transmission method in a WLANsystem including a relay device according to an embodiment of thepresent invention;

FIG. 13 is a conceptual diagram showing a data transmission method in aWLAN system including a relay device according to an embodiment of thepresent invention;

FIG. 14 is a flowchart showing a data transmission method in a WLANsystem including a relay device according to another embodiment of thepresent invention;

FIG. 15 is a conceptual diagram showing a first data transmission methodin a WLAN system including a relay device according to anotherembodiment of the present invention;

FIG. 16 is a conceptual diagram showing a second data transmissionmethod in a WLAN system including a relay device according to anotherembodiment of the present invention;

FIG. 17 is a flowchart showing a data transmission method in a WLANsystem including a relay device according to a further embodiment of thepresent invention; and

FIG. 18 is a conceptual diagram showing a data transmission method in aWLAN system including a relay device according to a further embodimentof the present invention.

BEST MODE

The present invention may be variously changed and may have variousembodiments, and specific embodiments will be described in detail belowwith reference to the attached drawings.

However, it should be understood that those embodiments are not intendedto limit the present invention to specific disclosure forms and theyinclude all changes, equivalents or modifications included in the spiritand scope of the present invention.

The terms such as “first” and “second” may be used to describe variouscomponents, but those components should not be limited by the terms. Theterms are merely used to distinguish one component from othercomponents. A first component may be designated as a second componentand a second component may be designated as a first component in thesimilar manner, without departing from the scope based on the concept ofthe present invention. The term “and/or” includes a combination of aplurality of related items or any of the plurality of related items.

It should be understood that a representation indicating that a firstcomponent is “connected” or “coupled” to a second component may includethe case where the first component is connected or coupled to the secondcomponent with some other component interposed therebetween, as well asthe case where the first component is “directly connected” or “directlycoupled” to the second component. In contrast, it should be understoodthat a representation indicating that a first component is “directlyconnected” or “directly coupled” to a second component means that nocomponent is interposed between the first and second components.

The terms used in the present specification are merely used to describespecific embodiments and are not intended to limit the presentinvention. A singular expression includes a plural expression unless adescription to the contrary is specifically pointed out in context. Inthe present specification, it should be understood that the terms suchas “include” or “have” are merely intended to indicate that features,numbers, steps, operations, components, parts, or combinations thereofare present, and are not intended to exclude a possibility that one ormore other features, numbers, steps, operations, components, parts, orcombinations thereof will be present or added.

Unless differently defined, all terms used here including technical orscientific terms have the same meanings as the terms generallyunderstood by those skilled in the art to which the present inventionpertains. The terms identical to those defined in generally useddictionaries should be interpreted as having meanings identical tocontextual meanings of the related art, and are not interpreted as beingideal or excessively formal meanings unless they are definitely definedin the present specification.

Hereinafter, preferred embodiments of the present invention will bedescribed in detail with reference to the attached drawings. For easyunderstanding of the entire part of the invention in the followingdescription of the present invention, the same reference numerals areused to designate the same or similar elements throughout the drawings,and repeated descriptions of the same components will be omitted.

Throughout the present specification, a station (STA) denotes anyfunctional medium that includes medium access control (MAC) conformingto the IEEE 802.11 standards and a physical layer interface for awireless medium. Stations may be classified into a station (STA) that isan access point (AP) and a station (STA) that is a non-AP. The stationthat is an AP may be simply called an access point (AP), and the stationthat is a non-AP may be simply called a terminal.

A ‘station (STA)’ may include a processor and a transceiver, and mayfurther include a user interface, a display device, etc. The processordenotes a unit devised to generate a frame to be transmitted over awireless network or process a frame received over the wireless network,and may perform various functions to control the station (STA). Thetransceiver denotes a unit that is functionally connected to theprocessor and is devised to transmit and receive a frame over thewireless network for the station (STA).

An ‘access Point (AP)’ may denote a centralized controller, a basestation (BS), a radio access station, a Node B, an evolved Node B, arelay, a Mobile Multihop Relay (MMR)-BS, a Base Transceiver System(BTS), a site controller, etc., and may include some or all of thefunctions thereof.

A ‘terminal (i.e. non-AP)’ may denote a Wireless Transmit/Receive Unit(WTRU), User Equipment (UE), a User Terminal (UT), an Access Terminal(AT), a Mobile Station (MS), a mobile terminal, a subscriber unit, aSubscriber Station (SS), a wireless device, a mobile subscriber unit,etc., and may include some or all of the functions thereof.

Here, the terminal may denote a desktop computer capable ofcommunication, a laptop computer, a tablet PC, a wireless phone, amobile phone, a smart phone, a smart watch, smart glasses, an e-bookreader, a Portable Multimedia Player (PMP), a portable game console, anavigation device, a digital camera, a Digital Multimedia Broadcasting(DMB) player, a digital audio recorder, a digital audio player, adigital picture recorder, a digital picture player, a digital videorecorder, a digital video player, etc.

FIG. 1 is a block diagram showing an embodiment of a station forperforming methods according to the present invention.

Referring to FIG. 1, a station 10 may include at least one processor 11,memory 12, and a network interface device 13 connected to a network 20and configured to perform communication. The station 10 may furtherinclude an input interface device 14, an output interface device 15, anda storage device 16. The components included in the station 10 may beconnected to each other through a bus 17, and may then performcommunication with each other.

The processor 11 may execute program instructions stored in the memory12 and/or the storage device 16. The processor 11 may denote a centralprocessing unit (CPU), a graphics processing unit (GPU), or an exclusiveprocessor for performing the methods according to the present invention.Each of the memory 12 and the storage device 16 may be implemented as avolatile storage medium and/or a nonvolatile storage medium. Forexample, the memory 12 may be implemented as read only memory (ROM)and/or random access memory (RAM).

The embodiments of the present invention are applied to a WLAN systemconforming to the IEEE 802.11 standards, and may also be applied toother communication systems as well as the WLAN system conforming to theIEEE 802.11 standards.

For example, the embodiments of the present invention may be applied tothe mobile Internet such as a Wireless Personal Area Network (WPAN), aWireless Body Area Network (WBAN), Wireless Broadband Internet (WiBro),or Worldwide Interoperability for Microwave Access (Wimax), a secondgeneration (2G) mobile communication network such as a Global System forMobile communication (GSM) or Code Division Multiple Access (CDMA), a 3Gmobile communication network such as Wideband Code Division MultipleAccess (WCDMA) or CDMA2000, a 3.5G mobile communication network such asHigh-Speed Downlink Packet Access (HSDPA) or High-Speed Uplink PacketAccess (HSUPA), a 4G mobile communication network such as Long-TermEvolution (LTE) or LTE-Advanced, or a 5G mobile communication network.

FIG. 2 is a conceptual diagram showing an embodiment of theconfiguration of a WLAN system conforming to IEEE 802.11.

Referring to FIG. 2, the WLAN system conforming to IEEE 802.11 mayinclude at least one basic service set (BSS). The BSS denotes a set ofstations (STA 1, STA 2(AP 1), STA 3, STA 4, STA 5(AP 2), STA 6, STA 7,STA 8) which are successfully synchronized with each other and arecapable of communicating with each other, and is not a concept meaning aspecific area.

BSSs may be classified into an infrastructure BSS and an independent BSS(IBSS). Here, BSS 1 and BSS 2 denote infrastructure BSSs and BSS 3denotes an IBSS.

BSS 1 may include a first terminal STA 1, a first access point STA 2 (AP1) for providing a distribution service, and a distribution system (DS)for connecting multiple access points STA 2(AP 1) and STA 5(AP 2) toeach other. In BSS 1, the first access point STA 2 (AP 1) may manage thefirst terminal STA 1.

BSS 2 may include a third terminal STA 3, a fourth terminal STA 4, asecond access point STA 5 (AP 2)) for providing a distribution service,and a distribution system (DS) for connecting the multiple access pointsSTA 2(AP 1) and STA 5(AP 2) to each other. In the BSS 2, the secondaccess point STA 5 (AP 2) may manage the third terminal STA 3 and thefourth terminal STA 4.

BSS 3 denotes an IBSS operating in an ad-hoc mode. In the BSS 3, thereis no access point that functions as a centralized management entity.That is, in the BSS 3, terminals STA 6, STA 7, and STA 8 are managed ina distributed manner. In the BSS 3, all of the terminals STA 6, STA 7,and STA 8 may denote mobile terminals, and access to the distributionsystem (DS) is not permitted, thus constituting a self-containednetwork.

The access points STA 2(AP 1) and STA 5(AP 2) may provide access to thedistribution system (DS) via a wireless medium for the terminals STA 1,STA 3, and STA 4 connected thereto. Communication between the terminalsSTA 1, STA 3, and STA 4 in the BSS 1 or BSS 2 is generally performed viathe access point STA 2 (AP 1) or STA 5 (AP 2), but direct communicationmay be performed between the terminals STA 1, STA 3, and STA 4 when adirect link is set up therebetween.

Multiple infrastructure BSSs may be connected to each other through thedistribution system (DS). The multiple BSSs connected through thedistribution system (DS) are called an extended service set (ESS). Theentities included in the ESS, that is, STA 1, STA 2(AP 1), STA 3, STA 4,and STA 5(AP 2), are capable of communicating with each other, and anyterminal STA 1, STA 3, or STA 4 may move from a single BSS to anotherBSS while performing seamless communication in the same ESS.

The distribution system (DS) is a mechanism for allowing one accesspoint to communicate with another access point. In accordance with theDS, the access point may transmit frames for terminals coupled to a BSSmanaged thereby, or may transmit frames for any terminal that has movedto another BSS. Further, the access point may transmit and receiveframes to and from an external network, such as a wired network. Such aDS is not necessarily a network and is not limited in its form as longas it is capable of providing a predetermined distribution servicedefined in the IEEE 802.11 standards. For example, the distributionsystem may be a wireless network such as a mesh network, or a physicalstructure for connecting the access points to each other.

Each terminal (STA) in the infrastructure BSS may be associated with anaccess point (AP). When associated with the access point (AP), theterminal (STA) may transmit and receive data.

FIG. 3 is a flowchart showing a terminal association procedure performedin an infrastructure BSS.

Referring to FIG. 3, the STA association procedure performed in theinfrastructure IBSS may be chiefly divided into the step of probing anAP (probe step), the step of performing authentication with the probedAP (authentication step), and the step of associating with the AP withwhich authentication has been performed (association step).

The terminal (STA) may first probe neighboring APs using a passivescanning method or an active scanning method. When the passive scanningmethod is used, the terminal (STA) may probe neighboring APs byoverhearing the beacons transmitted from the APs. When the activescanning method is used, the STA may probe neighboring APs bytransmitting a probe request frame and receiving a probe response framewhich is a response to the probe request frame from the APs.

When neighboring APs are detected, the STA may perform the step ofperforming authentication with each detected AP. In this case, the STAmay perform the step of performing authentication with multiple APs.Authentication algorithms conforming to the IEEE 802.11 standards may beclassified into an open system algorithm for exchanging twoauthentication frames with each other and a shared key algorithm forexchanging four authentication frames with each other.

Based on the authentication algorithms conforming to the IEEE 802.11standards, the STA may transmit an authentication request frame andreceive an authentication response frame, which is a response to theauthentication request frame, from each AP, thus completingauthentication with each AP.

When authentication has been completed, the STA may perform the step ofassociating with the AP. In this case, the STA may select a single APfrom among the APs with which authentication has been performed, and mayperform the step of associating with the selected AP. That is, the STAmay transmit an association request frame to the selected AP and receivean association response frame, which is a response to the associationrequest frame, from the selected AP, thus completing association withthe selected AP.

The WLAN system denotes a local area network in which multiplecommunication entities conforming to the IEEE 802.11 standards mayexchange data with each other in a wirelessly connected state.

FIG. 4 is a conceptual diagram showing the infrastructure BSS of a WLANsystem.

Referring to FIG. 4, the infrastructure BSS may include a single accesspoint (AP) and multiple terminals STA 1 and STA 2. The AP may transmit abeacon frame including a service set ID (SSID), which is a uniqueidentifier, in a broadcast manner. The beacon frame may provideinformation about the presence and association of the AP to terminalsthat are not associated with the AP, and may notify the terminalsassociated with the AP of the presence of data that is transmitted to aspecific terminal.

Each terminal that is not associated with the AP may probe the AP usinga passive scanning method or an active scanning method, and may acquireassociation information from the probed AP. In the case of the passivescanning method, the terminal may probe the AP by receiving a beaconframe from the AP. In the case of the active scanning method, theterminal may probe the AP by transmitting a probe request frame andreceiving a probe response frame, which is a response thereto, from theAP.

Each terminal that is not associated with the AP may attempt to performauthentication with a specific AP based on association informationacquired from the beacon frame or the probe response frame. A terminalthat has succeeded in authentication may transmit an association requestframe to the corresponding AP, and the AP, having received theassociation request frame, may transmit an association response frameincluding the AID of the terminal to the terminal. Via the aboveprocedure, the terminal may be associated with the AP.

FIG. 5 is a block diagram showing an embodiment of a hierarchical AIDstructure.

Referring to FIG. 5, in the IEEE 802.11 standards, an AID having ahierarchical structure may be used to efficiently manage multipleterminals. An AID assigned to a single terminal may be composed of apage ID, a block index, a sub-block index, and a terminal index (STAindex). The group to which the terminal belongs (i.e. a page group, ablock group, or a sub-block group) may be identified using informationabout individual fields.

FIG. 6 is a block diagram showing an embodiment of the structure of atraffic indication map (TIM) information element (IE).

Referring to FIG. 6, the TIM IE may include an element ID field, alength field, a delivery traffic indication message (DTIM) count field,a DTIM period field, a bitmap control field, and a partial virtualbitmap field. That is, the TIM IE includes information required toindicate a bit corresponding to the AID of a terminal when data to betransmitted to the terminal is buffered in the AP, and this informationmay be encoded into the bitmap control field and the partial virtualbitmap field.

FIG. 7 is a block diagram showing an embodiment of the structure of aTIM encoded on a block basis.

Referring to FIG. 7, in the IEEE 802.11 standards, the TIM may beencoded on a block basis. A single encoding block may include a blockcontrol field, a block offset field, a block bitmap field, and at leastone sub-block field.

The block control field may denote the encoding mode of the TIM. Thatis, the block control field may represent a block bitmap mode, a singleAID mode, an offset+length+bitmap (OLB) mode, or an inverse bitmap mode.The block offset field may represent the offset of an encoded block. Theblock bitmap field may represent a bitmap indicating the location of thesub-block in which an AID bit is set. The sub-block bitmap field mayrepresent a bitmap indicating the location of an AID in the sub-block.

FIG. 8 is a flow diagram showing an embodiment of a datatransmission/reception procedure.

Referring to FIG. 8, an access point (AP) may transmit a beacon frameincluding a TIM IE in a broadcast manner. A terminal (STA) operating ina power saving mode (PSM) may be awakened at intervals of a beaconperiod, in which a DTIM count becomes 0, and may receive a beacon frame.The terminal (STA) is configured to, when a bit corresponding to its AIDis set to ‘1’ in the TIM included in the received beacon frame, transmita power save (PS)-Poll frame (or a trigger frame) to the AP, thusnotifying the AP that the STA is ready to receive data. Upon receivingthe PS-Poll frame (or the trigger frame), the AP may transmit a dataframe to the corresponding STA.

In the WLAN system, communication entities (i.e. access points,terminals, etc.) share a wireless channel and contend with otherentities to access the wireless channel based on a carrier sensemultiple access (CSMA)/collision avoidance (CA) scheme. First, eachcommunication entity may check the occupied state of the wirelesschannel using a physical channel sensing scheme and a virtual channelsensing scheme before accessing the wireless channel.

The physical channel sensing scheme may be implemented via channelsensing, which detects whether energy of a predetermined level or moreis present in the wireless channel. When energy of a predetermined levelor more is detected using the physical channel sensing scheme, theterminal may determine that the wireless channel is occupied by anotherterminal, and thus may perform again channel sensing after waiting for arandom backoff time. Meanwhile, when energy of less than a predeterminedlevel is detected using the physical channel sensing scheme, theterminal may determine that the wireless channel is in an idle state,and may then access the corresponding wireless channel and transmit asignal through the wireless channel.

The virtual channel sensing scheme may be implemented by setting apredicted channel occupation time using a network allocation vector(NAV) timer. In the WLAN system, upon transmitting a frame, acommunication entity may write the time required to complete thetransmission of the corresponding frame in the duration field of theheader of the frame. When normally receiving a certain frame through thewireless channel, the communication entity may set its own NAV timerbased on a value in the duration field of the header of the receivedframe. When receiving a new frame before the NAV timer has expired, thecommunication entity may update the NAV timer based on the value in theduration field of the header of the newly received frame. When the NAVtimer has expired, the communication entity may determine that theoccupation of the wireless channel has been released, and may thencontend for access to a wireless channel.

The communication entity may support multiple data rates of a physicallayer depending on various modulation schemes and various channel codingrates. Generally, a high data rate for the physical layer enables alarge amount of data to be transmitted during a short wireless channeloccupation time, but requires high signal quality. In contrast, a lowdata rate for the physical layer enables data to be transmitted even atlow signal quality, but requires a relatively long wireless channeloccupation time.

Since the resources of the wireless channel are shared betweencommunication entities, the overall capacity of the WLAN system may beincreased only when the maximum amount of data is transmitted during thetime for which a specific communication entity occupies the wirelesschannel. That is, the overall capacity of the WLAN system may beincreased when the terminal transmits and receives data to and from theAP at the highest possible data rate for the physical layer. The highestdata rate for the physical layer may be realized when signal quality issufficiently secured owing to a short distance between the AP and theterminal. If the terminals are located far away from the AP, the datarate of the physical layer becomes low, thus resulting in the reductionof the overall capacity of the WLAN system.

In the WLAN system for providing a communication service to multiplesensor terminals located over a wide area, there may occur the casewhere data cannot be transmitted to the entire area using only thesignal output of a single AP. That is, sensor terminals that cannot besupported with a communication service may be present. Meanwhile, sincea low-power sensor terminal has low signal output, the range in whichthe WLAN system is capable of transmitting uplink data may be furthernarrowed.

In particular, since a terminal located in the coverage boundary of theAP exhibits poor signal quality, the terminal performs communicationwith the AP at a low data rate of the physical layer. Therefore, theoverall capacity of the WLAN system is drastically decreased. Further,when using the low data rate of the physical layer, the low-powerterminal must be awakened for a much longer time in order to transmitthe same amount of data, thus increasing power consumption.

FIG. 9 is a conceptual diagram showing a WLAN system including relaydevices.

Referring to FIG. 9, a master access point (master-AP: M-AP), a firstrelay device R1, a second relay device R2, and a fifth terminal STA 5may constitute a master BSS. The first relay device R1, a first terminalSTA 1, and a second terminal STA 2 may constitute a first relay BSS. Thesecond relay device R2, a third terminal STA 3, and a fourth terminalSTA 4 may constitute a second relay BSS. The relay devices R1 and R2 maybe located at the place where signal quality between the master accesspoint (M-AP) and the terminals STA 1, STA 2, STA 3, and STA 4 isdeteriorated. The first relay device R1 may relay data transmittedbetween the master access point (M-AP) and the first and secondterminals STA 1 and STA 2. The second relay device R2 may relay datatransmitted between the master access point (M-AP) and the third andfourth terminals STA 3 and STA 4. That is, the physical area of themaster access point (M-AP) may be extended via the relay devices R1 andR2.

FIG. 10 is a block diagram showing the logical configuration of a relaydevice.

Referring to FIG. 10, the relay device may include a relay terminal(R-STA), functioning as a master access point (M-AP), and a relay accesspoint (R-AP), functioning as an access point for terminals in anextended area.

The relay terminal (R-STA) may probe the master access point (M-AP) byreceiving a beacon frame or a probe response frame transmitted from themaster access point (M-AP) according to the same procedure as a normalterminal. Thereafter, the relay terminal (R-STA) may sequentiallyperform a procedure for authentication with the probed master accesspoint (M-AP) and a procedure for association with the M-AP.

The relay terminal (R-STA) may relay data transmitted between the masteraccess point (M-AP) and an end terminal. In this case, the relayterminal (R-STA) may relay data that is transmitted using a 4-addressfield. The 4-address field includes a destination address (DA) fieldindicating the address of the final destination of data, a sourceaddress (SA) field indicating the address of the place where the datawas generated, a transmitter address (TA) field indicating the addressof the communication entity that physically transmits a frame containingthe data, and a receiver address (RA) field indicating the address ofthe communication entity that is to physically receive the framecontaining the data.

For example, when desiring to transmit data to an end terminal via arelay device, the master access point (M-AP) may configure and transmitthe header address field of a data frame as follows.

-   -   DA field: address of end terminal    -   SA field: address of master access point (M-AP)    -   TA field: address of master access point (M-AP)    -   RA field: address of relay device

The relay terminal (R-STA) may forward a data frame received from therelay access point (R-AP) to the master access point (M-AP), and mayforward a data frame received from the master access point (M-AP) to therelay access point (R-AP).

When the relay terminal (R-STA) and the master access point (M-AP) areassociated with each other and a transfer path is acquired, the relayaccess point (R-AP) may periodically transmit a beacon frame includingan identifier (SSID) identical to that of the master access point(M-AP). Also, the relay access point (R-AP) may transmit a proberesponse frame in response to a probe request frame from the endterminal, transmit an authentication response frame in response to anauthentication request frame from the end terminal, and transmit anassociation response frame in response to an association request framefrom the end terminal. That is, the relay access point (R-AP) mayperform the same function as the master access point (M-AP).

An end terminal located near the relay device may be connected to arelay-AP (R-AP) located closer to the end terminal than the masteraccess point (M-AP) and may secure high signal quality, thus enablingdata to be transmitted at a high data rate of the physical layer.

The relay access point (R-AP) may generate a beacon frame including anindicator indicating that the R-AP itself is a communication entity forrelaying data transmitted between the master access point (M-AP) and theend terminal, and may transmit the generated beacon frame. Such anindicator may be defined either using one bit in the beacon frame orusing the address field of the master access point (M-AP).

The relay access point (R-AP) may transmit a data frame using a4-address field in the same way as the relay terminal (R-STA).Alternatively, the relay access point (R-AP) may transmit a data frameusing a 3-address field (SA=TA, RA, and DA) when the SA field isidentical to the TA field.

FIG. 11 is a conceptual diagram showing a data transmission method in aWLAN system including a relay device.

Referring to FIG. 11, a master access point (M-AP) and a relay device Rmay constitute an M-BSS and the relay device R and a first terminal STA1 may constitute an R-BSS. The master access point (M-AP) mayperiodically transmit a master beacon frame including a trafficindication map (TIM) in a broadcast manner. Generally, since the relaydevice R associated with the master access point (M-AP) is operated inan awake mode, the master access point (M-AP) may transmit a data frameto the relay device (R) at any time. Here, the master access point(M-AP) may transmit a data frame to the relay device R when a channel isin an idle state during a distributed interframe space (DIFS) and acontention window (CW) based on a random access procedure. When the dataframe has been successfully received, the relay device R may transmit anacknowledge (ACK) frame, as a response to the data frame, to the masteraccess point (M-AP).

Meanwhile, if it is determined that the data frame received from themaster access point (M-AP) is a data frame to be transmitted to thefirst terminal STA 1, the relay device R may generate a TIM includingthe identifier information of the first terminal STA 1 (i.e. a TIM inwhich a bit corresponding to the AID of the STA 1 is set to ‘1’ may begenerated), and may generate a relay beacon frame including the TIM. Therelay device R may transmit the relay beacon frame in a broadcastmanner.

The first terminal STA 1, having received the relay beacon frame, mayrecognize that its own AID is included in the TIM of the relay beaconframe (i.e., a bit corresponding to the AID of the first terminal STA 1is set to ‘1’), and may then notify the relay device R that the firstterminal STA 1 is ready to receive a data frame by transmitting aPS-Poll frame (or a trigger frame) to the relay device R. At this time,the first terminal STA 1 may transmit the PS-Poll frame (or the triggerframe) to the relay device R when the channel is in an idle state duringa DIFS and a CW based on a random access procedure.

When the PS-Poll frame (or the trigger frame) is received, the relaydevice R may transmit an ACK frame as a response thereto andsubsequently transmit a data frame to the first terminal STA 1, or mayomit the transmission of an ACK frame and immediately transmit a dataframe to the first terminal STA 1. When the data frame has beensuccessfully received, the first terminal STA 1 may transmit an ACKframe, which is a response to the data frame, to the relay device R.

Meanwhile, the master access point may transmit data to the relay deviceon high power. Therefore, since a wireless link between the masteraccess point and the relay device has high quality, the master accesspoint may transmit data to the relay device at high speed. However,since the end terminal connected to the relay device is operated on lowpower, a wireless link between the relay device and the end terminal haslow quality due to a limitation in the intensity of a transmittedsignal, or the like. Therefore, the relay device cannot transmit data tothe end terminal at high speed.

In particular, when the master access point transmits data to the endterminal via the relay device, the data may be transmitted from themaster access point to the relay device at high speed because the relaydevice is operated in an awake mode. However, since the end terminal isoperated in a power saving mode (PSM), the relay device may transmitdata to the end terminal only when the end terminal is awakened. Thatis, the transmission of data from the relay device to the end terminalmay be delayed. Therefore, during the procedure for transmittingdownlink data via the relay device, data buffering may occur, and bufferoverflows may occur in the relay device when a large amount of data istransmitted from the master access point to the relay device.

To prevent the loss of data caused by buffer overflows, the relay devicemay request the master access point to suspend or resume thetransmission of downlink data.

FIG. 12 is a flowchart showing a data transmission method in a WLANsystem including a relay device according to an embodiment of thepresent invention, and FIG. 13 is a conceptual diagram showing a datatransmission method in a WLAN system including a relay device accordingto an embodiment of the present invention.

Referring to FIGS. 12 and 13, a master access point (M-AP) mayconstitute an M-BSS, and a relay device R may constitute an R-BSS. Themaster access point (M-AP) may periodically transmit a master beaconframe including a TIM in a broadcast manner (S100). Generally, since therelay device R is operated in an awake mode, the master access point(M-AP) is configured to, when it has data to be transmitted to the relaydevice R, transmit a data frame to the relay device R if a channel is inan idle state during a DIFS and a CW based on a random access procedure(S110).

The relay device R, having successfully received the data frame, maygenerate an ACK frame that requests the suspension of the transmissionof a data frame when residual space is not present in a buffer and nomore data frames can be received. That is, the relay device R mayindicate that it is operated in a doze mode by setting a powermanagement (PM) bit of a flow control (FC) field included in the MACheader of the ACK frame to ‘1’. The relay device R may transmit an ACKframe (i.e. PM bit=1), which is a response to the data frame, to themaster access point (S120). After transmitting the ACK frame, the relaydevice R may not be actually operated in a doze mode. That is, the ACKframe may be used to notify the master access point (M-AP) that therelay device R is in the state in which no more data frames can bereceived.

When the ACK frame is received, the master access point (M-AP) maydetermine that the relay device R has successfully received the dataframe. Further, the master access point (M-AP) may determine that therelay device R is operated in a doze mode because the PM bit of the ACKframe is set to ‘1’. That is, the master access point (M-AP) maydetermine that the relay device R is in the state in which no more dataframes can be received. Therefore, the master access point (M-AP) maynot transmit a data frame to the relay device R until the relay device Ris capable of receiving a data frame (i.e. until the relay device R isoperated in an awake mode).

Meanwhile, the master access point (M-AP) may periodically transmit amaster beacon frame including a TIM in a broadcast manner (S130). Ifthere is data to be transmitted to the relay device R, the master accesspoint (M-AP) may generate a TIM including the identifier of the relaydevice R (i.e. a TIM in which a bit corresponding to the AID of therelay device R is set to ‘1’ may be generated), and may transmit amaster beacon frame including the TIM in a broadcast manner (S140).

The relay device R, having received the master beacon frame, mayrecognize that data to be transmitted thereto is buffered in the masteraccess point (M-AP) because the bit corresponding to the AID of therelay device R is set to ‘1’ in the TIM included in the master beaconframe. When residual space sufficient to receive a data frame is presentin the buffer, the relay device R may generate a PS-Poll frame (or atrigger frame) that requests the resumption of the transmission of adata frame. That is, the relay device may indicate that it is operatedin an awake mode by setting a PM bit of a FC field included in the MACheader of the PS-Poll frame (or the trigger frame) to ‘0’. The relaydevice R may transmit the PS-Poll frame (or the trigger frame) in whichthe PM bit is set to ‘0’ to the master access point (M-AP) (S150). Atthis time, the relay device R may transmit the PS-Poll frame (or thetrigger frame) to the master access point (M-AP) when the channel is inan idle state during a DIFS and a CW based on a random access procedure.

When the PS-Poll frame (or the trigger frame) is received, the masteraccess point (M-AP) may transmit an ACK frame, as a response thereto, tothe relay device R (S160). Here, the master access point (M-AP) maydetermine that the relay device R is in the state in which data framescan be received (i.e. the state of an awake mode) because the PM bit ofthe PS-Poll frame (or the trigger frame) is set to ‘0’. Therefore, themaster access point (M-AP) may transmit a data frame to the relay deviceR (S170). When the data frame is received, the relay device R maytransmit an ACK frame, as a response thereto, to the master access point(M-AP) (S180).

Meanwhile, when it is determined that the data frame received from themaster access point (M-AP) is a data frame to be transmitted to the endterminal belonging to the R-BSS, the relay device R may generate a TIMincluding the identifier information of the end terminal (i.e. a TIM inwhich a bit corresponding to the AID of the end terminal is set to ‘1’may be generated), and may generate a relay beacon frame including theTIM. The relay device R may transmit the relay beacon frame in abroadcast manner.

The end terminal, having received the relay beacon frame, may recognizethat its own AID is included in the TIM of the relay beacon frame (i.e.a bit corresponding to the AID of the end terminal is set to ‘1’), andmay then notify the relay device R that the end terminal is ready toreceive a data frame by transmitting a PS-Poll frame (or a triggerframe) to the relay device R. When the PS-Poll frame (or the triggerframe) is received, the relay device R may transmit an ACK frame as aresponse thereto and subsequently transmit a data frame to the endterminal or, alternatively, may omit the transmission of an ACK frameand immediately transmit a data frame to the end terminal. When the dataframe has been successfully received, the end terminal may transmit anACK frame, which is a response thereto, to the relay device R.

FIG. 14 is a flowchart showing a data transmission method in a WLANsystem including a relay device according to another embodiment of thepresent invention, FIG. 15 is a conceptual diagram showing a first datatransmission method in a WLAN system including a relay device accordingto another embodiment of the present invention, and FIG. 16 is aconceptual diagram showing a second data transmission method in a WLANsystem including a relay device according to another embodiment of thepresent invention.

Referring to FIGS. 14 to 16, a master access point (M-AP) may constitutean M-BSS, and a relay device R may constitute an R-BSS. The masteraccess point (M-AP) may periodically transmit a master beacon frameincluding a TIM in a broadcast manner (S200).

Meanwhile, when residual space is not present in a buffer, and no moredata frames can be received, the relay device R may generate a null dataframe that requests the suspension of the transmission of a data frame.That is, the relay device R may indicate that it is operated in a dozemode by setting a PM bit of an FC field included in the MAC header ofthe null data frame to ‘1’. The relay device R may transmit the nulldata frame to the master access point (M-AP) when a channel is in anidle state during a DIFS and a contention window (CW) based on a randomaccess procedure (S210). The relay device R may not be actually operatedin a doze mode after transmitting the null data frame in which the PMbit is set to ‘1’. That is, the null data frame may be used to notifythe master access point (M-AP) that the relay device R is in the statein which no more data frames can be received.

When the null data frame is received, the master access point (M-AP) maytransmit an ACK frame, as a response thereto, to the relay device R(S220). The master access point (M-AP) may determine that the relaydevice R is operated in a doze mode because the PM bit of the null dataframe is set to ‘1’. That is, the master access point (M-AP) maydetermine that the relay device R is in the state in which no more dataframes can be received. Therefore, the master access point (M-AP) maynot transmit a data frame to the relay device R until the relay device Ris capable of receiving a data frame (i.e. until the relay device R isoperated in an awake mode).

Meanwhile, the master access point (M-AP) may periodically transmit amaster beacon frame including a TIM in a broadcast manner (S230). Whenthere is data to be transmitted to the relay device R, the master accesspoint (M-AP) may generate a TIM including the identifier of the relaydevice R (i.e. a TIM in which a bit corresponding to the AID of therelay device R is set to ‘1’ may be generated), and may transmit amaster beacon frame including the TIM in a broadcast manner (S240).

The relay device R, having received the master beacon frame, mayrecognize that data to be transmitted thereto is buffered in the masteraccess point (M-AP) because a bit corresponding to the AID of the relaydevice R is set to ‘1’ in the TIM included in the master beacon frame.When residual space sufficient to receive a data frame is present in thebuffer, the relay device R may generate a null data frame that requeststhe resumption of the transmission of a data frame. That is, the relaydevice R may indicate that it is operated in an awake mode by setting aPM bit of an FC field included in the MAC header of the null data frameto ‘0’. The relay device R may transmit the null data frame in which thePM bit is set to ‘0’ to the master access point (M-AP)(S250). At thistime, the relay device R may transmit the null data frame to the masteraccess point (M-AP) when a channel is in an idle state during a DIFS anda CW based on a random access procedure.

Alternatively, the relay device R may generate, instead of a null dataframe, a PS-Poll frame (or a trigger frame) that requests the resumptionof the transmission of a data frame. That is, the relay device R mayindicate that it is operated in an awake mode by setting a PM bit of anFC field included in the MAC header of the PS-Poll frame (or the triggerframe) to ‘0’. The relay device R may transmit the PS-Poll frame (or thetrigger frame) in which the PM bit is set to ‘0’ to the master accesspoint (M-AP).

When the null data frame (or the PS-Poll frame or the trigger frame) isreceived, the master access point (M-AP) may transmit an ACK frame, as aresponse thereto, to the relay device R (S260). At this time, the masteraccess point (M-AP) may determine that the relay device R is in thestate in which data frames can be received (i.e. the state of a awakemode) because the PM bit of the null data frame (or the PS-Poll frame orthe trigger frame) is set to ‘0’. Therefore, the master access point(M-AP) may transmit a data frame to the relay device R (S270). When thedata frame is received, the relay device R may transmit an ACK frame, asa response thereto, to the master access point (M-AP) (S280).

Meanwhile, if it is determined that the data frame received from themaster access point (M-AP) is a data frame to be transmitted to the endterminal belonging to the R-BSS, the relay device R may generate a TIMincluding the identifier information of the end terminal (i.e. a TIM inwhich a bit corresponding to the AID of the end terminal is set to ‘1’may be generated), and may generate a relay beacon frame including theTIM. The relay device R may transmit the relay beacon frame in abroadcast manner.

The end terminal, having received the relay beacon frame, may recognizethat its own AID is included in the TIM of the relay beacon frame (i.e.a bit corresponding to the AID of the end terminal is set to ‘1’), andmay then notify the relay device R that the end terminal is ready toreceive a data frame by transmitting a PS-Poll frame (or a triggerframe) to the relay device R. When the PS-Poll frame (or the triggerframe) is received, the relay device R may transmit an ACK frame as aresponse thereto and subsequently transmit a data frame to the endterminal or, alternatively, may omit the transmission of an ACK frameand immediately transmit a data frame to the end terminal. When the dataframe has been successfully received, the end terminal may transmit anACK frame, which is a response thereto, to the relay device R.

FIG. 17 is a flowchart showing a data transmission method in a WLANsystem including a relay device according to a further embodiment of thepresent invention, and FIG. 18 is a conceptual diagram showing a datatransmission method in a WLAN system including a relay device accordingto a further embodiment of the present invention.

Referring to FIGS. 17 and 18, a master access point (M-AP) mayconstitute an M-BSS and a relay device R may constitute an R-BSS. Themaster access point (M-AP) may periodically transmit a master beaconframe including a TIM in a broadcast manner (S300). Meanwhile, the relaydevice R may generate a transmission suspend frame that requests thesuspension of the transmission of a data frame when residual space isnot present in a buffer and no more data frames can be received.

The following Table 1 shows the values and meanings of a relay actionfield used in a transmission suspend frame and in a transmission resumeframe that requests the resumption of the transmission of a data frame.

TABLE 1 Field value Meaning 1 Data transmission suspend 2 Datatransmission resume 3-255 Reserved

The following Table 2 shows the configuration of a transmission suspendframe.

TABLE 2 Sequence Information 1 Action category (relay device) 2 Relayaction (data transmission suspend) 3 Suspend duration

The transmission suspend frame may include an action category field anda relay action (data transmission suspend) field. Also, the transmissionsuspend frame may further include a suspend duration field. The actioncategory field may indicate that a certain action is the operation ofthe relay device R, the relay action field may indicate that thesuspension of the transmission of a data frame is requested, and thesuspend duration field may indicate a suspend duration during which thetransmission of a data frame is suspended.

That is, the relay device R may generate a transmission suspend framethat includes an action category field indicating its own operation anda relay action field indicating that the suspension of the transmissionof a data frame is requested. Alternatively, the relay device maygenerate a transmission suspend frame that includes an action categoryfield indicating its own operation, a relay action field indicating thatthe suspension of the transmission of a data frame is requested, and asuspend duration field indicating a suspend duration (interval) duringwhich the transmission of a data frame is suspended.

The relay device R may transmit the transmission suspend frame to themaster access point (M-AP) (S310). When the transmission suspend frameis received, the master access point (M-AP) may determine that the relaydevice R is in the state in which no more data frames can be received.Therefore, the master access point (M-AP) may not transmit a data frameto the relay device R until the relay device R is capable of receiving adata frame. That is, the master access point (M-AP) may not transmit adata frame to the relay device R until a transmission resume frame thatrequests the resumption of the transmission of a data frame is receivedfrom the relay device R. Further, when a suspend duration field isincluded in the transmission suspend frame, the master access point(M-AP) may not transmit a data frame to the relay device R during asuspend duration indicated by the suspend duration field. If the suspendduration indicated by the suspend duration field has elapsed, the masteraccess point (M-AP) may transmit a data frame to the relay device R evenbefore a transmission resume frame is received from the relay device R.

Meanwhile, the master access point (M-AP) may periodically transmit amaster beacon frame including a TIM in a broadcast manner (S320). Ifthere is data to be transmitted to the relay device R, the master accesspoint (M-AP) may generate a TIM including the identifier of the relaydevice R (i.e. a TIM in which a bit corresponding to the AID of therelay device R is set to ‘1’ may be generated), and may transmit amaster beacon frame including the TIM in a broadcast manner (S330).

The relay device R, having received the master beacon frame, mayrecognize that data to be transmitted thereto is buffered in the masteraccess point (M-AP) because the bit corresponding to the AID of therelay device R is set to ‘1’ in the TIM included in the master beaconframe. When residual space sufficient to receive a data frame is presentin the buffer, the relay device R may generate a transmission resumeframe that requests the resumption of the transmission of a data frame.

The following Table 3 shows the configuration of a transmission resumeframe.

TABLE 3 Sequence Information 1 Action category (relay device) 2 Relayaction (data transmission resume)

The transmission resume frame may include an action category field and arelay action (data transmission resume) field. The action category fieldmay indicate that a certain action is the operation of the relay deviceR, and the relay action field may indicate that the resumption of thetransmission of a data frame is requested. That is, the relay device Rmay generate a transmission resume frame that includes an actioncategory field indicating its own operation, and a relay action fieldindicating that the resumption of the transmission of a data frame isrequested.

The relay device R may transmit the transmission resume frame to themaster access point (M-AP) (S340). Further, when a transmission suspendframe including a suspend duration field has been transmitted, the relaydevice R may transmit a transmission resume frame to the master accesspoint (M-AP) even before the suspend duration indicated by the suspendduration field elapses. When the transmission resume frame is received,the master access point (M-AP) may determine that the relay device R isin the state in which a data frame can be received. Therefore, themaster access point (M-AP) may transmit a data frame to the relay deviceR (S350). When the data frame is received, the relay device R maytransmit an ACK frame, as a response thereto, to the master access point(M-AP) (S360).

Meanwhile, when it is determined that the data frame received from themaster access point (M-AP) is a data frame to be transmitted to the endterminal belonging to the R-BSS, the relay device R may generate a TIMincluding the identifier information of the end terminal (i.e. a TIM inwhich a bit corresponding to the AID of the end terminal is set to ‘1’may be generated), and may generate a relay beacon frame including theTIM. The relay device R may transmit the relay beacon frame in abroadcast manner.

The end terminal, having received the relay beacon frame, may recognizethat its own AID is included in the TIM of the relay beacon frame (i.e.a bit corresponding to the AID of the end terminal is set to ‘1’), andmay then notify the relay device R that the end terminal is ready toreceive a data frame by transmitting a PS-Poll frame (or a triggerframe) to the relay device R. When the PS-Poll frame (or the triggerframe) is received, the relay device R may transmit an ACK frame as aresponse thereto and subsequently transmit a data frame to the endterminal or, alternatively, may omit the transmission of an ACK frameand immediately transmit a data frame to the end terminal. When the dataframe has been successfully received, the end terminal may transmit anACK frame, which is a response thereto, to the relay device R.

In accordance with the present invention, a master access point mayextend a service area via a relay device. Since a terminal may secure agood quality link via the relay device, data can be transmitted at highspeed. That is, the relay device is used, and thus the efficiency of useof a wireless channel may be improved and the amount of power consumedby the terminal may be reduced.

Further, when residual space is not present in a buffer, the relaydevice may request the master access point to suspend the transmissionof data. By means of this, buffer overflows may be prevented fromoccurring in the relay device.

The embodiments of the present invention may be implemented in the formof program instructions that are executable via various types ofcomputer means, and may be recorded on a computer-readable medium. Thecomputer-readable medium may include program instructions, data files,and data structures solely or in combination. Program instructionsrecorded on the computer-readable medium may have been speciallydesigned and configured for the embodiments of the present invention, ormay be known to or available to those who have ordinary knowledge in thefield of computer software.

Examples of the computer-readable storage medium include all types ofhardware devices specially configured to store and execute programinstructions, such as read only memory (ROM), random access memory(RAM), and flash memory. The hardware devices may be configured tooperate as one or more software modules in order to perform theoperation according to embodiments of the present invention, and viceversa. Examples of the program instructions include machine languagecode, such as code created by a compiler, and high-level language codeexecutable by a computer using an interpreter or the like.

Although the present invention has been described with reference to theembodiments, those skilled in the art will appreciate that the presentinvention can be modified and changed in various forms, withoutdeparting from the spirit and scope of the invention as disclosed in theaccompanying claims.

1. A method for data transmission being performed by a relay device forrelaying data transmitted between a master access point and an endterminal, comprising: generating a suspend request frame that requestssuspension of transmission of a data frame from the master access pointto the relay device; and transmitting the suspend request frame to themaster access point.
 2. The method of claim 1, wherein the suspendrequest frame is an acknowledge (ACK) frame that is a response to a dataframe received from the master access point, and the ACK frame includesinformation indicating that the relay device is operated in a doze mode.3. The method of claim 1, wherein the suspend request frame is a nulldata frame that includes information indicating that the relay device isoperated in a doze mode.
 4. The method of claim 1, wherein the suspendrequest frame includes information about a suspend duration during whichtransmission of a data frame is suspended.
 5. A method for datatransmission being performed by a relay device for relaying datatransmitted between a master access point and an end terminal,comprising: generating a resume request frame that requests resumptionof transmission of a data frame from the master access point to therelay device; and transmitting the resume request frame to the masteraccess point.
 6. The method of claim 5, further comprising: receiving adata frame, as a response to the resume-request frame, from the masteraccess point; and transmitting an acknowledge (ACK) frame, as a responseto the data frame, to the master access point.
 7. The method of claim 5,wherein the resume request frame is a power save (PS)-Poll frame or atrigger frame indicating that the relay device is operated in an awakemode.
 8. The method of claim 5, wherein the resume request frame is anull data frame that includes information indicating that the relaydevice is operated in an awake mode.
 9. The method of claim 5, whereintransmitting the resume request frame to the master access point isconfigured to transmit the resume request frame to the master accesspoint when it is determined that data to be transmitted to the relaydevice is buffered in the master access point, based on a beacon framereceived from the master access point.